1. Field of the Invention
Exemplary aspects of the present invention generally relate to a decelerator, a drive device including same, and an image forming apparatus incorporating the drive device.
2. Description of the Background Art
In general, image forming apparatuses, such as printers, facsimile machines, and copiers, are equipped with an image bearing member such as a photoreceptor. In such image forming apparatuses, as the image bearing member rotates, image forming processes such as charging, exposure, development, image transfer and so forth are carried out.
A drive source such as a motor is used to rotate the image bearing member. In general, the speed of rotation of the drive source is greater than a required speed of rotation of the image bearing member.
Conventionally, in order to reduce revolution of the motor, a decelerator using a gear is used. A traction oil is used as a lubricant suitable for transmission of rotational friction of the motor.
In the decelerator using the gear, when rotational loads are applied on the image bearing member during charging, exposure, development, image transfer, and so forth, backlash of the gear may cause fluctuation in the rotation speed of the image bearing member. Consequently, imaging quality is degraded.
To counteract this problem, a decelerator using the planetary roller is proposed. Because this decelerator does not utilize the gear, fluctuation in the rotation speed of the image bearing member can be prevented. However, a drawback of this approach is that the configuration using the planetary roller tends to be complicated, thus preventing reduction in the size and the cost of the apparatus.
In the decelerator using the gear, a flywheel is proposed to suppress fluctuation of the rotation speed of the image bearing member. In particular, drive force between a driving side and a driven side is transmitted by friction between a surface of a drive roller and a surface of a driven roller. It is advantageous in that fluctuation in the rotation speed of the flywheel due to backlash can be prevented.
In view of the above, the configuration described above may be employed in the decelerator so as to reduce the speed by a rotation ratio of the drive roller and the driven roller. However, a drawback of this approach is that because drive transmission is performed simply by using the friction between the surface of the drive roller and the surface of the driven roller, it is difficult to prevent fluctuation in the rotation speed, for the following reason.
In order to perform drive transmission using friction, the drive roller and the driven roller need to press against each other to maintain frictional force therebetween. In the meantime, in order to prevent fluctuation of the rotation speed, it is necessary to prevent undesirable drift of the drive roller and the driven roller. However, it is difficult to achieve both the desirable frictional force and prevention of fluctuation of the rotation speed at the same time.
When the drive roller and the driven roller press against each other in order to maintain a certain frictional force, rotation axes of the drive roller and the driven roller may bend, causing rotation of the rollers to fluctuate (decenter). As a result, the rotation speed fluctuates. If, on the other hand, the drive roller and the driven roller slightly contact or contact each other with only a little force, drive force is not properly transmitted, causing insufficient drive transmission.